Systems, apparatuses and methods for determining blood pressure

ABSTRACT

The present disclosure is directed to apparatuses, systems and methods for measuring time-varying radar cross section (RCS) of an artery of a patient, which may be used to determine blood pressure of a patient. In some embodiments, an apparatus is provided which comprises a radio-frequency (RF) transceiver for generating RF waves, and at least one sensor configured for positioning on or adjacent the skin of a patient, and at least one of transmitting the RF waves into tissue of the patient and receiving RF wave reflections from at least one artery located within the tissue. The apparatus may further comprise a processor having computer instructions operating thereon configured to cause the processor to determine an RF arterial pulse waveform based on the received RF wave reflections. The time-varying radar cross section (RCS) comprises the RF arterial pulse waveform. This may be in turn correlated to blood pressure of the patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of and claims priority under 35USC §119 to: U.S. provisional patent application Ser. No. 61/935,958filed Feb. 5, 2014, entitled “Systems and Methods for Determining BloodPressure Using Electromagnetic Waves.”

FIELD OF THE DISCLOSURE

Embodiments of the current disclosure are directed toward blood pressuremeasurement, and more particularly, systems and methods for bloodpressure measurement utilizing electromagnetic radiation/waves.

BACKGROUND OF THE DISCLOSURE

Radio-frequency (RF) electromagnetic radiation has been used fordiagnosis and imaging of body tissues, examples of which may be found inPCT publication no. WO2011/067623, US publication nos. 2009/0299175 and2009/0240133, and U.S. Pat. Nos. 4,926,868 and 5,766,208.

WO 2011/067623 is understood to be directed to a diagnostic apparatusthat includes an antenna, which directs RF electromagnetic waves into aliving body and generates signals responsively to the waves that arescattered from within the body. US patent publication no. 2009/0240133is understood to be directed to a radio apparatus and method fornon-invasive, thoracic radio interrogation of a subject for thecollection of hemodynamic, respiratory and/or other cardiopulmonaryrelated data. US patent publication no. 2009/0299175, is understood tobe directed to a method and apparatus for determining and tracking thelocation of a metallic object in a living body, using a radar detectoradapted to operate on a living body. U.S. Pat. No. 4,926,868 isunderstood to be directed to a method and apparatus for cardiachemodynamic monitoring based on the complex field amplitudes ofmicrowaves propagated through and scattered by thoracic cardiovascularstructures, particularly the heart chambers, as a function of timeduring the cardiac cycle.

However, none of these references are understood to discloseascertaining blood pressure utilizing radio-frequency (RF) waves.

SUMMARY OF SOME OF THE EMBODIMENTS

Embodiments of the present disclosure present methods, systems andapparatuses techniques for continuous Non-Invasive Blood Pressure(cNIBP) measurement are discussed in the present disclosure (in someembodiments, such measurements may be non-continuous). In suchembodiments, cNIBP measurements may be accomplished by determining, forexample, Pulse Wave Velocity (PWV), which can be used as, for example, ameasure of arterial stiffness. In some instances, PWV corresponds to thevelocity of propagation of the arterial pressure pulse between pointsalong the arterial tree, which may depend on, amongst other things, theblood pressure. Accordingly, determination of PWV and/or the pulsetransit time (PTT) between points along the arterial tree may provideinformation on the blood pressure in the arteries.

In some embodiments, one or more sensors may be used to determine thePTT, and/or the pulse wave arrival time, which may also be referred toas the pulse arrival time (PAT), which may be different from the PTT.For example, there may be a delay between the generation of the pulse bythe ventricular muscle and the opening of the aortic valve. In someinstances, when using sensors such as an electrocardiogram (ECG) deviceand a photo-plethysmograph (PPG), the PAT may correspond to the delaybetween the ECG's QRS peak (e.g., R-peak) and a point on the PPG signalrepresenting the pressure pulse at a peripheral artery. Examples of suchsensors comprise ECGs, PPGs, radio-frequency (RF) sensors, etc. In someembodiments, the RF sensor allows for determination/estimation of thearterial pulse waveform which may provide clinical information such as,but not limited to, arterial stiffness, PWV, cardiac output, cNIBPmeasurements, etc.

In some embodiments, an apparatus and a method for measuringtime-varying radar cross section (RCS) of an artery of a patient aredisclosed. The apparatus comprises a RF transceiver for generating RFwaves, at least one sensor configured for positioning on or adjacent theskin of a patient, and at least one of transmitting the RF waves intotissue of the patient and receiving RF wave reflections from at leastone artery located within the tissue. In some implementations, the atleast one sensor comprises at least one antennae. In some instances, itmay be configured with flexibility that allows the sensor to conform tothe skin of the patient. The apparatus also comprises a processor havingcomputer instructions operating thereon configured to cause theprocessor to execute some or all steps of the method disclosed herein.The steps of the method comprise determining an RF arterial pulsewaveform based on the received RF wave reflections, where thetime-varying RCS comprises the RF arterial pulse waveform.

In some embodiments, the method also comprises the steps of correlatingthe time-varying RCS to a time-varying diameter of the at least oneartery, conditioning the RF arterial pulse waveform using at least oneradar echo from a specific range, and adapting the specific range to theat least one artery. In some implementations, the steps also includeconditioning the RF arterial pulse waveform using band pass filtering,and determining a time location of at least one of a peak of the RFarterial pulse waveform, the first derivative peak, and other pointsmarking an RF-arterial-pulse-arrive-time (RE-PAT). In some embodiments,the methods include the steps of characterizing the RF arterial pulsewaveform. For example, characterizing may comprise determining a timingof the dicrotic notch of the waveform.

In some embodiments, the apparatus comprises an ECG sensor configuredfor positioning on the body of the patient for receiving signalscorresponding to an ECG waveform, where signals from the ECG sensor aresynchronized with the RF wave reflections. In some instances, the methodincludes determining arterial-pulse-arrival-time (PAT) based on a timedifference between the RF-PAT and an R-peak of the ECG waveform. Theapparatus may also comprise an ECG sensor configured for positioning onthe body of the patient for receiving signals corresponding to an ECGwaveform. Further, the apparatus may include the at least one sensorpositioned to receive RF wave reflections from the aorta of the patient,where signals from the ECG sensor are synchronized with the RF wavereflections. In some instances, the method may comprise the step ofdetermining an R-peak of the ECG waveform, and determining a timedifference between the RF-arterial-pulse-arrival-time (RF-PAT) and theR-peak to determine a pre-ejection period (PEP). In addition, thecomputer instructions may be further configured to cause the processorto determine PTT, where PTT is determined by subtracting PEP from PAT.

In some embodiments, the at least one sensor may be configured forsensing RF wave reflections corresponding to PAT to each of twodifferent arterial tree locations. In some instances, the methodincludes the step of determining the PAT at each location anddetermining the difference between the PAT at the two locations so as todetermine a PTT. The two different arterial tree locations may bediscerned based on depth resolution of the tissue. In some embodiments,the apparatus may comprise a second sensor, where the first sensor isconfigured for sensing RF wave reflections corresponding to PAT at afirst arterial tree location, and where the second sensor is configuredfor sensing signals corresponding to PAT at a second arterial treelocation. In some embodiments, the method includes determining the PATat each location and determining the difference between the PAT at thetwo locations so as to determine the PTT. In such embodiments, the firstarterial tree location and the second arterial tree location comprisedifferent locations on the same arterial tree. In some instances, thefirst arterial tree location and the second arterial tree locationcomprise different arterial trees. In some instances, the first arterialtree location and the second arterial tree location may comprisedifferent arterial trees on different areas of the body of a patient.

In some embodiments, the method comprises the step of utilizing an EGGwaveform of the patient to synchronize the first and second sensors.Further, it includes gating the time measurement between the first andsecond sensors, where one sensor gates the measurement of the other.

In some of the embodiments disclosed above, the second sensor comprisesa photo-plethysmograph (PPG) sensor or an RF sensor. In addition, themethod includes the step of determining the patient's blood pressure asa function of PTT, where parameters used to determine NT are calibratedfor the patient. In some embodiments, the method includes determiningarterial PWV, where PWV equals the propagation distance of the arterialpulse wave divided by PTT.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIGS. 1A-B shows an example embodiment of determination of thepre-ejection period (PEP) from electrocardiogram and radio-frequencysignal measurements.

FIG. 2 shows a diagram depicting an example arterial pulse waveform.

FIG. 3 shows the measurement of arterial pulse waveform from a changing(e.g., time-varying) radar cross section of an artery during cardiacpressure cycle.

FIG. 4 illustrates an example placement of radio-frequency sensors overthe thorax.

FIG. 5 depicts an example schematic diagram of the components of theapparatus for measuring time-varying radar cross section (RCS) of anartery disclosed herein.

DETAILED DESCRIPTION OF SOME OF THE EMBODIMENTS

In some embodiments of the present disclosure, systems and methods fordetermining blood pressure using electromagnetic waves are presented.For example, RF sensors (e.g., antenna) may be utilized to receiveand/or transmit RF signals. In some instances, the RF signal waveformcan be continuous or based on step frequency. In some implementations,the signals may have a wide range of frequencies, for example, the RFfrequency may range from about 300 MHz to about 3 GHz. In someembodiments, the RF sensor can achieve a range (e.g., depth) resolutionthat allows filtering of reflections from relevant depth in a patient'sbody. For example, the sensor may allow penetration of a few centimetersinto the body, facilitating its usage for a variety of arteries (e.g.anterior tibial, popliteal, brachial, carotid, etc.).

In some implementations, the RF sensors may be used in conjunction withother sensors/devices, such as (for example) an ECG sensor/device and/ora PPG sensor, to determine PTT and/or PAT of a pulse wave in an artery.In some embodiments, there may be a time lapse between the ventricularpolarization and the opening of the aortic valve—i.e., the Pre-EjectionPeriod (PEP)—which, in some embodiments, corresponds to the time ittakes for the myocardium to raise sufficient pressure to open the aorticvalve and start pushing blood out of the ventricle. In some instances,the effects of the PEP may be significant in determining blood pressurelevels.

In some embodiments, the PTT to some point along the arterial tree(e.g., peripheral location in the arterial system) may be represented asthe difference between the arrival time of the pulse at the point andthe pre-ejection period, i.e., PTT=PAT−PEP. Upon determining orestimating the PTT, in some embodiments, the PWV may then be calculatedbased on the distance the pulse traveled to arrive at the point and theestimated/determined PTT. In some implementations, blood pressure valuessuch as systolic and/or diastolic values can be determinednon-invasively from the PWV and/or the PTT. For example, lineartransformations relating the systolic blood pressure (SBP) and diastolicblood pressure (DBP) to the PTT may be expressed as follow:

SBP=(a×PTT)+b,

DBP=(c×PTT)+d,

where the coefficients a, b, c and d can be calibrated for each patient.In some embodiments, other types of transformations may be used tocalculate blood pressures. For example, for a model that assumesconstant artery thickness and radius, blood pressure P may be expressedas P=a×ln(PTT)+b, where, again a and b are constants to be calibratedfor each patient. In any case, in some embodiments, obtaining PTT, orconversely PWV of a pulse in an artery, may lead to the determination ofblood pressure levels in the artery.

Usage of an RF Sensor and an ECG for Determining PEP Correction

In some embodiments, RF waves may be used to locate the time of theopening of the aortic valve. For example, the reflected electromagneticsignal (with sensors located in the appropriate place, and optionallyafter appropriate filtering) may provide information on the opening ofthe aortic valve, and hence can be used in conjunction with the ECGsignals that represent the activation of the ventricles, for determiningthe PEP. Once PEP is obtained, in some embodiments, the calculation ofthe PTT follows from the relation PTT=PAT−PEP upon finding PAT. In someinstances, PAT can be found by comparing the simultaneous detection ofECG signals to that of the PPG signals, which represent the activationof the pulses at the ventricles and arrival of the pulses at theperipheral arteries, respectively. For example, the comparison maycorrespond to the delay between the ECG's QRS peak (i.e., R-peak) and apoint on the PPG signal representing the pressure pulse at a peripheralartery. In such embodiments, one or more PPG sensors may be located neara peripheral artery (e.g., finger, ear-lobe, etc.), and one or more RFsensors (e.g., antenna) may be located so that the antennae receivesreflections from the heart, for example, at the sternum. The heartsignals can be isolated by a combination of range and Doppler filteringof the RF signals. For example, the RF signal may be filtered to isolateheart reflections from the relevant depth, and may also be filtered toremove reflections from static objects. As to the ECG signals, theR-peak time may be determined from the ECG signals. FIG. 1 shows anexample embodiment of PEP correction estimation 103 from the timedifference between the ECG R-peak 102 and the RF signal pulse 101.

In some embodiments, the RF sensor can be utilized to obtain thearterial pulse waveform, which may provide clinical information such as,but not limited to, arterial stiffness, PWV, cardiac output, cNIBPmeasurements, and the like. For example, the sensor may scan the crosssection of objects in its view, which may include an artery. As such, asthe pulse wave is propagating through the artery, the RF sensor maymeasure the changing radar cross section of the artery. In suchinstances, the changing arterial cross section is related to the pulsewave, and accordingly the arterial pulse waveform maybe determined fromthe changing cross section. An example arterial pulse wave 201 obtainedusing this method is depicted in FIG. 2. This method has severaladvantages in that in obtaining the arterial pulse waveform, it is atleast non-invasive, allows penetration into the body, and/or can beoperated with little or no expertise.

FIG. 3 shows the measurement of arterial pulse waveform from a changing(e.g., time-varying) RCS of an artery during cardiac pressure cycle,according to some embodiments. For example, during a cardiac cycle, anRF radar sensor 301 may generate and transmit RF waves 303 towards anartery 302 which may be located at a certain depth from the RF sensor301 corresponding to a measurement range 306 a. In some embodiments,some or all of the transmitted waves 303 may be reflected back to the RFsensor 301. In some instances, the RF sensor 301 may transmit the RFwaves 303 continuously or non-continuously. During the cardiac cycle,the diameter of the artery 302 may be varying over time, e.g., 305 a and305 b, and as a result the RCS of the artery 302 obtained by the RFsensor 301 changes over time as well. From the measurements of thevarying RCS, in some implementations, an arterial pulse waveform 304representing the pulse wave propagating through the artery may bedetermined. In turn, from the arterial pulse waveform 304, a variety ofclinical information such as but not limited to arterial stiffness, PWV,cardiac output, blood pressure measurements (continuous ornon-continuous) may be obtained. In some embodiments, the reflected echomay be modulated by the artery over the course of the cardiac cycle, andinformation from the reflected echo can be used to determine/estimatethe arterial pulse waveform 304. For example, the measurement range 306a may change over the course of the cardiac cycle (e.g., 306 a and 306b), leading to changes in the phase of the reflected waves. In suchinstances, such information can be utilized to determine/estimate thearterial pulse waveform 304.

Usage of RF Waves for Determining PAT

In some embodiments, RF waves may be used to determine the PAT. Asdiscussed above, the ECG signals represent the activation of theventricles, i.e., the onset of the pulse wave. As such, a determinationof the arrival of the pulse at a location on an artery may allow for anestimation/determination of the PAT by comparing the ECG signals withtime of arrival for the pulse. In some embodiments, the location may beat a peripheral artery (e.g., fingers, ear lobes, etc.). In someembodiments, the location may be at a depth inside a body, which asdiscussed above is one advantage of using RF signals. For example, theRF sensor can be located in a variety of places on the body, whichallows for the ability of the RF waves to penetrate into a particulardepth into the body. In some embodiments, this may allow for choosing anartery for observation (i.e., not necessarily in the finger or earlobe).The RF reflections may be used to identify the time of arrival of thepulse wave to the chosen artery, and the PAT may be determined from thetime difference between the ECG R-peak and the RF signal pulse arrivaltime.

Usage of Two RF Sensors for Determining PTT

In some embodiments, the PTT of the pulse can be determined if the timesof arrival of the pulse at two distinct locations can be measured. Thisfollows because the PEP values of the pulse that originated at the sameventricle but arrived at the two different locations is the same, andaccordingly, the difference in PAT for the two locations is the same asthe difference in PTT of the pulse to the two distinct locations. Forexample, FIG. 4 shows two RF sensors 401 and 402 located at differentpositions on the body (e.g., the sternum and the thorax, two suitablelocations along the leg, etc.) can be used to sense the pulse wave goingthrough arteries close to each RF sensor. In some embodiments, the RFsensors may be incorporated into clothing (e.g., stockings, shirts,etc.), chest straps, wrist straps, skin patches, and/or the like.

In some embodiments, for each of the RF sensors, the RF signal may befiltered to isolate the reflections from the relevant depth and toremove reflections from static objects. In such embodiments, the PTT maybe determined as the time difference between the pulse wave arrivaltimes as measured by the two RF sensors. It is worth noting that the twoRF sensors, in some embodiments, may be synchronized. An example way toachieve synchronization may be by using two ECG sensors, where the Rpeak can be viewed as the synchronizing marker.

Usage of an RF Sensor and a PPG for Determining PTT

As discussed above, the PTT of the pulse can be determined if the timesof arrival of the pulse at two distinct locations can be measured. Inthe previous embodiments, the two locations were disclosed to be at theperipheries of arteries, for example, at the sternum and the thorax, attwo suitable locations along the leg, etc. In other embodiments, bothlocations may not be on the peripheries of arteries as discussed above.For example, one of them can be at the periphery of an artery, and theother can be at a depth inside the body. For example, two co-locatedsensors, an RF sensor and a PPG sensor, may detect, respectively, anartery located inside the body and a peripheral artery (e.g., on afinger, ear lobes, etc.). In some embodiments, the RF sensor may be usedto penetrate into the body and reflections from a specific depth in thebody can be isolated by processing the RF echoes. The PPG sensor (e.g.,used in reflective mode) may be used to measure reflections fromsuperficial arteries, and the pulse wave of these arteries may then bemeasured by the PPG. Since the types of observed arteries have adifferent path from the heart, in some implementations, they thereforemay include a different travel time. In some embodiments, thisdifference can be indicative of the blood pressure. For example, thesensors can be located on the thorax, where reflected RF echoes from thelungs (for example) can be isolated, and pulse waves from arteries goingthrough the lung may be measured in this way. According to someembodiments, the pulse waves from the RF sensor and from the PPG arecompared, with the time delay between them determined to be TimeDelay=(PTT from the heart to the lung arteries)−(PTT from the heart tothe thorax superficial arteries). As disclosed above, this timedifference can be used to determine the blood pressure.

Usage of a Single RF Sensor for Determining PTT

In some embodiments, the determination of the PTT of a pulse may beaccomplished by a single RF sensor if the times of arrival of the pulseat two distinct locations can be measured using the single sensor.Above, example embodiments have been disclosed where the two distinctlocations are at peripheries of arteries, and other embodiments whereone location is at a periphery of artery and the other at a depth insidethe body. In some embodiments, the two locations may be inside the bodyat different depths. For example, the single RF sensor may be located ina position where it receives signals for deciphering different arteriesat different depths in the body. For example, the sensor may detectpulse waves arriving at different arteries belonging to differentbranches at different depths in an arterial tree. In such embodiments,the sensor may measure their arrival times at the different depths, anddetermine/estimate the PTT from the time difference between the arrivaltimes.

FIG. 5 depicts an example schematic diagram of the components of theapparatus for measuring time-varying radar cross section (RCS) of anartery disclosed herein. For example, the apparatus may comprise one ormore RF sensors 501. Further, it may also include an ECG sensor 502configured for receiving signals corresponding to an ECG waveform. Insome instances, the apparatus may also contain a PPG device 503. Thedevices/sensors such as the RF sensors 501, the ECG sensor 502, the PPGdevice 503, etc., may receive signals from the body of a patient (e.g.,from arteries). In some embodiments, these sensors/devices may transmitdata/information corresponding to the received signals to a processor504 configured for executing computer instructions to act on thetransmitted data/information. Further, the processor 504 may receiveother input (e.g., patient data, variables (e.g., temperature, time,etc.), and/or the like), and upon executing computer instructions withsome or more of the received input, in some embodiments, the processor504 may generate outputs 505 such as, but not limited to, arterial pulsewaveform, blood pressure measurements, etc. These outputs may bepresented via any suitable media (e.g., printer, database, display,audio, and the like).

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

At least some of the embodiments disclosed above, in particular at leastsome of the methods/processes disclosed, may be realized in circuitry,computer hardware, firmware, software, and combinations thereof (e.g., acomputer system). Such computing systems, may include PCs (which mayinclude one or more peripherals well known in the art), smartphones,specifically designed medical apparatuses/devices and/or othermobile/portable apparatuses/devices. In some embodiments, the computersystems are configured to include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network (e.g., VPN, Internet). The relationshipof client and server arises by virtue of computer programs running onthe respective computers and having a client-server relationship to eachother.

Some embodiments of the disclosure (e.g., methods and processesdisclosed above) may be embodied in a computer program(s)/instructionsexecutable and/or interpretable on a processor, which may be coupled toother devices (e.g., input devices, and output devices/display) whichcommunicate via wireless or wired connect (for example).

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be an example and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure. Stillother embodiments of the present disclosure are patentable over priorart references for expressly lacking one or more features disclosed inthe prior art (i.e., claims covering such embodiments may includenegative limitations).

Any and all references to publications or other documents, including butnot limited to, patents, patent applications, articles, webpages, books,etc., presented anywhere in the present application, are hereinincorporated by reference in their entirety. One or more features and/orembodiments disclosed in one or more of incorporated by referencedocuments herein can also be combined with one or morefeatures/embodiments of the present disclosure to yield yet furtherembodiments (of the present disclosure).

Moreover, all definitions, as defined and used herein, should beunderstood to control over dictionary definitions, definitions indocuments incorporated by reference, and/or ordinary meanings of thedefined terms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

1-48. (canceled)
 49. An apparatus for measuring time-varying radar crosssection (RCS) of an artery of a patient, comprising: a radio-frequency(RF) transceiver for generating RF waves; at least one sensor configuredfor positioning on or adjacent the skin of a patient, and at least oneof transmitting the RF waves into tissue of the patient and receiving RFwave reflections from at least one artery located within the tissue; anda processor having computer instructions operating thereon configured tocause the processor to: determine an RF arterial pulse waveform based onthe received RE wave reflections, wherein the time-varying radar crosssection (RCS) comprises the RF arterial pulse waveform, and correlatethe time-varying RCS to a time-varying diameter of the at least oneartery.
 50. The apparatus of claim 49, wherein the at least one sensorcomprises at least one antennae, and/or the at least one sensor isconfigured with flexibility to enable the at least one sensor to conformto the skin of the patient.
 51. The apparatus of claim 49, wherein thecomputer instructions are additionally configured to cause the processorto condition the RF arterial pulse waveform using at least one radarecho from a specific range.
 52. The apparatus of claim 49, wherein thecomputer instructions are additionally configured to cause the processorto condition the RF arterial pulse waveform using band pass filtering.53. The apparatus of claim 49, wherein the computer instructions areadditionally configured to cause the processor to characterize the RFarterial pulse waveform, characterizing the RF arterial pulse waveformincluding determining at least one or more of: a peak-to-peak amplitudeof the RF arterial pulse waveform; a time location of at least one of apeak of the RF arterial pulse waveform, a first derivative peak, andother points marking an RF-arterial-pulse-arrive-time (RF-PAT); and atiming of a dicrotic notch of the RF arterial pulse waveform.
 54. Theapparatus of claim 49, further comprising an ECG sensor configured forpositioning on the body of the patient for receiving signalscorresponding to an ECG waveform, wherein signals from the ECG sensorare synchronized with the RF wave reflections, and wherein the computerinstructions are additionally configured to cause the processor todetermine arterial-pulse-arrival-time (PAT) based on a time differencebetween an RF-arterial-pulse-arrive-time (RF-PAT) and an R-peak of theECG waveform.
 55. The apparatus of claim 49, further comprising an ECGsensor configured for positioning on the body of the patient forreceiving signals corresponding to an ECG waveform, wherein the at leastone sensor is positioned to receive RF wave reflections from the aortaof the patient, signals from the ECG sensor are synchronized with the RFwave reflections, and wherein the computer instructions are additionallyconfigured to cause the processor to determine an R-peak of the ECGwaveform, and determine a time difference between theRF-arterial-pulse-arrival-time (RF-PAT) and the R-peak to determine apre-ejection period (PEP).
 56. The apparatus of claim 55, wherein thecomputer instructions are additionally configured to cause the processorto determine an arterial-pulse-travel-time (PTT) by subtracting the PEPfrom PAT.
 57. The apparatus of claim 49, wherein the at least one sensoris configured for sensing RF wave reflections corresponding toarterial-pulse-arrival-time (PAT) to each of two different arterial treelocations, the two different arterial tree locations discerned based ondepth resolution of the tissue.
 58. The apparatus of claim 49, whereinthe at least one sensor is configured for sensing RF wave reflectionscorresponding to arterial-pulse-arrival-time (PAT) to each of twodifferent arterial tree locations, wherein the computer instructions areadditionally configured to cause the processor to determine anarterial-pulse-travel-time (PTT) by determining a difference between thePAT at the two different arterial tree locations.
 59. The apparatus ofclaim 49, wherein the computer instructions are additionally configuredto determine arterial pulse-wave velocity (PWV), wherein the PWV equalsa propagation distance of the arterial pulse wave divided by PTT.
 60. Anapparatus for measuring time-varying radar cross section (RCS) of anartery of a patient, comprising: a radio-frequency (RF) transceiver forgenerating RF waves; a first sensor and a second sensor configured forpositioning on or adjacent the skin of a patient; wherein the firstsensor is configured for sensing RF wave reflections corresponding toarterial-pulse-arrival-time (PAT) at a first arterial tree location, andthe second sensor is configured for sensing signals corresponding to PATat a second arterial tree location; and a processor having computerinstructions operating thereon configured to cause the processor to:determine the PAT at each location and determine the difference betweenthe PAT at the two locations so as to determine anarterial-pulse-travel-time (PTT).
 61. The apparatus of claim 60, whereinthe first arterial tree location and the second arterial tree locationinclude one of the following: different locations on the same arterialtree, different arterial trees, and different arterial trees ondifferent areas of the body of a patient.
 62. The apparatus of claim 60,wherein the computer instructions are additionally configured to causethe processor to utilize an ECG waveform of the patient to synchronizethe first and second sensors.
 63. The apparatus of claim 60, wherein thecomputer instructions are additionally configured to cause the processorto gate the time measurement between the first and second sensors,wherein one sensor gates the measurement of the other.
 64. The apparatusof claim 60, wherein the first sensor and/or the second sensor include aphoto-plethysmograph (PPG) sensor or an RF sensor.
 65. The apparatus ofclaim 60, wherein the computer instructions are additionally configuredto cause the processor to determine the patient's blood pressure as afunction of arterial-pulse-travel-time (PTT), wherein parameters used todetermine the PTT are calibrated for the patient.
 66. A method formeasuring time-varying radar cross section (RCS) of an artery of apatient, comprising: transmitting RF waves into a tissue of the patientat a first location; receiving RF wave reflections from at least oneartery located within the tissue via at least one sensor; determining anRF arterial pulse waveform based on the received RF wave reflections,wherein the time-varying radar cross section (RCS) comprises the RFarterial pulse waveform; and conditioning the RF arterial pulse waveformusing at least one radar echo from a specific range adapted to the atleast one artery.
 67. The method of claim 66, wherein the at least onesensor comprises a first sensor and a second sensor, the method furthercomprising: sensing, via the first sensor, RF wave reflectionscorresponding to arterial-pulse-arrival-time (PAT) at a first arterialtree location, sensing, via the second sensor, signals corresponding toPAT at a second arterial tree location, determining the PAT at eachlocation, and determining the difference between the PAT at the twolocations so as to determine the an arterial-pulse-travel-time (PTT).68. The method of claim 66, further comprising determining a timing of adicrotic notch of the RF arterial pulse waveform.
 69. The method ofclaim 67, further comprising determining a timing of a dicrotic notch ofthe RF arterial pulse waveform.